The present invention concerns air exhausting means, intended in particular for kitchens in catering industry or equivalent, said air exhausting means comprising an outer housing, an exhausting chamber provided with at least one suction aperture or grease filter unit, a collector chamber for gaseous impurities, and a blow chamber, in the vicinity of which a guide baffle may be disposed.
The ventilation of catering industry kitchens, grill bars or equivalent is very difficult to manage, as is well-known. From the kitchen equipment are released various waste heat loads, such as fumes, vapours, etc., which should be managed in order to achieve successful ventilation.
Ventilation of catering industry kitchens can be understood as a system of process ventilation. In a catering industry kitchen, the food preparation apparatus constitutes the locations where impure air is released. Good interior air conditions can be created only if the spreading of impurities released in the working area of the kitchen to that zone of the kitchen where persons are staying, and particularly their spread in the respiration air zone, can be prevented.
Presently, the details mentioned in the foregoing have been taken into account, and apparatus for kitchens in catering industry have been developed very intensively. With the means of prior art, endeavours are made to eliminate the produced waste heat and impure air in such a way that the waste heat and impure air cannot at all spread in the kitchen. To this type belongs apparatus such as washing machines and ovens, the vapours and fumes produced in them being removed directly from within the means to an air exhausting duct system. In this case, however, a so-called closed system is concerned.
However, all kitchen apparatus in catering industry cannot be directly connected to the air exhausting duct system so that the working conditions in the catering kitchen are not affected. This kind of equipment includes stoves, kettles, grid irons, grills, frying pans and fat baths. The impurities released from this kind of apparatus frequently enter the personnel's respiration air zone, thus impairing their working conditions. The distribution of fresh air to the respiration air zone is frequently an overwhelming task because the impurities are mixed with the intake air before it has reached the respiration air zone of the workers. Endeavours have been made to eliminate the drawbacks mentioned in the foregoing by constructing a so-called steam cowl over the kitchen apparatus, but the operation of the steam cowl appliances of existing art is unsatisfactory. The functioning of steam cowls depends on the degree of their encapsulation, on their shape, front face area, exhaust air quantity, and on the location of the suction aperture. In addition, the above factors are interdependent.
Recommendable front face velocities have been stated in pertinent literature for various local exhaust points. In catering industry kitchens, for the front face velocity, or the so-called capture velocity, a value 0.25 to 0.7 m/s per kitchen cowl front face area is recommended. At flow rate 0.25 m/s, only so-called slow flows carrying only little heat and vapours can be captured. With increasing convection, higher capture velocities are required.
It has been found in practice that the values mentioned in the foregoing are not applicable in designing because the exhaust air quantities would become excessive so that the required substitution air cannot be led into the kitchen space without incurring draught. Therefore, the designers have reduced the exhaust air quantities according to their own judgement, whereby the quantities of air used in catering industry kitchens have been made implementable.
When the front face velocity is reduced, the consequence is that part of the spoiled kitchen air can escape to the respiration air zone, owing to the reduction of the so-called capture velocity. Hereby, the kitchen cowl is no longer operative, and the humidity of the air and its temperature gradient become disadvantageous in the kitchen. The situation presented in the foregoing is still present in all types of air exhausting apparatus used in catering industry kitchens at present.
As to the state of art, reference is made to the Finnish Pat. No. 58971, the U.S. Pat. No. 4,286,572 and the Swedish publizicing print No. 7904443-4, in which some of the designs known in present art are disclosed.
The designs known in the art have numerous drawbacks. The designs are usually over-dimensioned as regards their exhaust air and marginal blowing quantities. The designs of prior art produce a blow jet, the shape of which is unsatisfactory. Likewise, the flow field is unfavourable, and the design of the margins and interior of the cowl is unsatisfactory. In the designs presently known, control of the air quantity is moreover difficult to accomplish. Furthermore, in the designs of prior art there is no possibility to adjust the grease filters by which the grease filtering efficiency could be influenced.